This invention relates to a means for measuring mass flow of fluent material such as liquids, gases and fluent solid material wherein the coriolis force is utilized as an indication of the mass flow. The flow meter includes U-shaped tubes which are vibrated while a fluent material to be measured flows through the tubes. The tubes are so constructed that the moment arm acted on by the coriolis force couple is increased so that the force couple may be more easily measured. The preferred embodiment of the flow meter includes two U-shaped flow tubes which are arranged to form a tuning fork. This arrangement allows for the tubes to be vibrated using much less force than is necessary with a single U-tube.
The patent to Poole, et al., U.S. Pat. No. 2,635,462 discloses a densometer wherein two hollow vibrating elements are arranged to form two tines of a tuning fork. Each element is made up of a set of two concentric flow tubes for forming a flow path through the densometer. The tines are vibrated and the natural frequency of the vibrations varies with the density of the material in the densometer. A feedback system for the vibrator is disclosed for measuring the density of the material flowing through the meter.
A densometer using U-shaped flow tubes for the tines of a tuning fork has also been constructed wherein the fluent material flows through an inlet port in a fixed member, into a first U-shaped loop, through the loop and back to the fixed member, through an innerconnecting flow means to a second U-shaped tube, through the second U-shaped tube back to the fixed member, and finally out through an outlet port in the fixed member. In this densometer, vibrations in the first U-tube set up sympathetic vibrations in the second U-tube to reduce the power necessary to cause the required oscillations in the tuning fork arrangement.
U.S. Pat. No. 3,355,944 to Sippin shows a U-shaped tube which may be vibrated. The coriolis force couple caused by the vibrations create a torque which is measured to determine the mass flow of the material flowing through the tube.
A coriolis type flow meter has been built which utilizes a U-shaped tube with its two open ends in a fixed member for one-half of the tuning fork. The other half of the tuning fork is formed by a metal bar with one end in the fixed member, and having the other end free to oscillate. The bar and the U-shaped tube are vibrated by means of an electromagnet fixed to the free end of the solid bar and magnetically pushing and pulling the intermediate or U portion of the tube.
The flow meter of the present invention uses a pair of spaced apart U-shaped tubes with their ends in a fixed member forming a tuning fork arrangement. In the preferred embodiment the U portion of the first tube includes a vibrating means for oscillating the U portion of the second tube. The frequency of the oscillations are adjusted until the U-shaped tubes vibrate a fixed displacement when a known material is flowing through the meter. The power needed to vibrate the U-shaped tubes a known displacement at a fixed frequency determines the density of an unknown fluent material flowing through the U-shaped tubes.
These flow tubes are also arranged such that the coriolis force couples cause opposite torques in each U-shaped tube. The inlets to the U-shaped tubes are spaced close together and the U-shaped tubes contain bent portions such that the moment arms acted on by the coriolis force couples is increased, thus making the meter's sensitivity to these coriolis forces much greater. Several embodiments of the vibrating tubes are also disclosed.